My view is divided on Decathlon. On the one hand they are a good one stop shop, competitively priced, and we all have to vote with our wallets undoubtedly, and especially for stuff for the kids or for stuff that I don't really need quality to last years, or don't want to spend a lot on, I use them. Stuff that is pretty basically functional too - free weights a good example, again, I use them. And non specialist stuff where the market is well stitched up by venture capitalists and conglomerates too...
where I'm less sure is the stuff where really, specialism is important. Climbing and caving gear is my main gripe but it extends to cycling too, and probably other stuff for those who know about it. The places where you really want advice over cost. This is where I hate them - like the Tesco effect on the high street, they'll basically drive the independent shops out of business. Want to try hanging in a harness before buying, need to know which bit of kit is good for your specific need based on experience, after sales advice and service, want a product that they don't sell? That's when you come unstuck. A good analogy is that my first job was in a specialist mountain shop, it was eventually closed due to soaring rents and an obvious commercial decision to attract the 'standard high street' into the city centre (the unit is a Subway now)... We had a lot of very loyal customers of c. 15 years, and we could sell them the stuff they really needed based on experience. We could sort out problems with kit outside warranty, and if you had a 20 year old ice axe that needed a new bolt or a spare discontinued pick, we probably had one or knew one that would work, we could probably lend you an out of print guidebook to a niche location too, or had climbed there and knew the local beta. Lots of towns had shops like this not too long ago, now they are pretty much all gone and even now, the remaining hardcore are going a bit corporate (Outside in Hathersage springs to mind).
I know it's the cost of progress, internet, rising costs, etc. but I still think its a lamentable shame